Genetically engineered mouse models are critical for the research programs of Koch Institute Members. They are used to probe the role of cancer genes in cell and developmental biology, investigate the mechanisms of tumor development, progression and metastasis, evaluate drug response and resistance, and test novel strategies and devices for tumor detection and drug delivery. The ES Cell & Transgenics Core is an Institutional Shared Resource that provides Koch Institute investigators with consultative advice, technical support and/or training in the production of engineered cells and mouse models. In the current period, the capabilities of this Core have been further expanded and enhanced. This includes moving into a larger, custom-designed space in the new Koch Institute building, the addition of new services and a reorganization of the staff to support novice users and provide project-customized services. Notably, in the same period, usage of the ES Cell & Transgenics Core by Center Members increased from 29% to 51%, including investigators from all four programs. Thus, this Shared Resource is essential to the success of the Koch Institute mission. In the upcoming period, the ES Cell & Transgenics Core will continue to offer a wide range of state-of-the-art services to support the research programs of Center Members. In spite of the significant expansion of services and usage, the requested CCSG budget for Year 44 is 13% lower than the requested and recommended budget in Year 39.